The rapid decrease in viscosity of liquids with increasing temperature is well-known. Ideally, for many applications (automobile lubricants, etc.) it would be desirable to solve this problem so that viscosity would be insensitive to temperature. Alternatively, it might be desirable to provide liquid systems whose viscosities actually increase with temperature. It is true that with selected polymeric additives, it has been possible to reduce substantially the viscosity change with temperature which does occur with most oils and similar systems. These polymer additives, known as viscosity index improvers (or V.I. Improvers) are generally high molecular weight polymers.
The way in which these additives function can be summarized very briefly. In effect, they perform two functions, i.e., thickening, which merely increases fluid viscosity; and Viscosity Index (V.I.) improvement, which corresponds to limited thickening at ambient temperatures and a correspondingly greater thickening at elevated temperatures. This can be accomplished by utilizing a polymeric additive which is poorly solvated by the liquid at ambient temperatures; however, at elevated temperatures the polymer is more highly solvated such that the polymer expands and is a relatively more effective thickner.
While these V.I. Improvers have proven successfully commercially, it is important to note that their effect at reducing viscosity changes with temperatures is rather mild. For a typical base oil containing a suitable V.I. Improver, the kinematic viscosity will still decrease by a factor of from 5 to 10 as the temperature increases from 30.degree. to 100.degree. C. Obviously, if it is desired to hold the viscosity roughly constant with such temperature changes. Current technology has not offered an appropriate additive system to solve this problem.
U.S. Pat. No. 3,396,136 describes how copolymers of alkenyl aromatic sulfonic acid, when properly neutralized, can be employed as thickeners for nonpolar solvents. Those metal sulfonate systems have been shown to be very effective; however, when employed as two component systems (i.e., ionic polymer plus nonpolar solvent), the variation of viscosity with increased temperature is very conventional and predictable. That is, the solution viscosity decreases markedly as temperature is increased.
U.S. Pat. No. 3,396,136 further teaches "in situ" neutralization of the sulfonic acid polymer which, under some conditions, can result in the availability of a small amount of polar cosolvent, i.e., a solvent for the sulfonate groups about equal in amount to the amount of sulfonate groups which are present. This amount of polar cosolvent is not within the limits of the instant invention, which only optionally requires amounts of the cosolvent (which interacts with the ionomeric groups of the ionomer copolymer) at levels which range from 10 to 600 times the molar equivalence of ionic groups. This level of cosolvent is about one to two orders of magnitude or more higher than employed in the cited art. In addition, the cited patent is restricted to aromatic sulfonate polymers. The instant invention describes other polymers such as sulfonated ethylene propylene terpolymers, which are a portion of the polymer complex.
U.S. Pat. No. 3,366,430 teaches the gelling of organic liquids by the interaction of polar "associative bonds" which includes hydrogen bonding and "ionic cross-linking". Again, this patent specifies that two components are necessary--the associating polymer (or polymers in some cases) and the nonpolar organic liquid. There is no mention of a third polar cosolvent except to point out that such polar liquids should not be present. Specifically, this patent states (Column 2, line 7) that the hydrocarbon liquids to which this invention is to be applied should not contain a substantial portion of a miscible protolytic liquid such as methanol. It is clear that the language of this patent limits this invention to gels and further, that any amount of polar liquids which are present to an extent where they disrupt those gels are undesirable. The instant invention is distinct from that cited in that amounts of such polar compounds, as will break up gel at ambient conditions, are required and in fact the most preferred state is free of any said gel at ambient conditions, are required and in fact that most preferred state is free of any said gel at ambient temperatures.
U.S. Pat. No. 3,679,382 teaches the thickening of aliphatic hydrocarbons with synthetic organic polymers which contain olefinically unsaturated copolymerizable acids, amides, hydroxacrylic esters, sulfonic acids, etc. It is emphasied in this patent (Column 3, line 72) that it is critical that in the preparation of such polymers, no surface active agent, catalyst or other additive be employed which introduces a metallic ion into the system. Therefore, it is preferred to employ ammonium or amine salts. It is clear that this invention (U.S. Pat. No. 3,679,382) specifically precludes the use of metallic counterions--and is directed towards amine or ammonium derivatives. Only metallic counterions are effective in the instant invention--and that, in fact, attempts to employ amine derivatives have not resulted in the results which are the objectives of this invention. Finally, this cited patent does describe (Column 7, lines 13-19) that the addition of alcohols will reduce the viscosity of the thickened hydrocarbon and alter flow characteristics thereof.
U.S. Pat. Nos. 3,931,021 and 4,118,361 describe the use of ionic polymers and required co-solvents in an organic liquid and V.I. Improvers. The instant invention represents an improvement over U.S. Pat. Nos. 3,931,021 and 4,118,361, and therefore provides a new dimension in viscosity control of hydrocarbon-based solvents. Specifically, it has been discovered that these complexes offer a different viscosity-temperature relationship than do the sulfonate ionomers previously disclosed. Furthermore, the types of ionic polymers previously described as viscosifiers for oils and low polarity diluents usually are effective thickeners at modest levels, but if one attempts to make a concentrate (10% polymer by weight) the resulting solution is too viscous to handle. The solutions described in this invention can have relatively low viscosities at high concentrations of polymer, yet maintain relatively high viscosities at low polymer concentrations. This change in the viscosity-concentration relationship is a fundamental discovery of potentially great practical relevance. Typically, solutions of ionomers display high viscosities at polymer concentrations near 1% or above, and at lower polymer concentrations display abnormally low viscosities. Consequently, such solutions are not efficient viscosifiers at polymer concentrations which are attractive from an economic viewpoint. At the same time concentrated solutions of such ionic polymers possess undesirably high viscosities precluding preparation of polymer concentrates from a practical standpoint. Currently such solutions display very steep viscosity-concentration profiles such that a modest change in polymer concentration results in a dramatic change of viscosity. In any practical application this behavior is extremely undesirable for a very slight change in concentration produces an impractical change in viscosity.
The instant invention describes a modification in the viscosity concentration profiles of ionomer solutions which moderates the change in viscosity with concentration such that this "knife-edge" characteristics is no longer manifested to the same degree. Furthermore, it is a consequence of this modification that high polymer concentrations can be prepared of such solutions with substantially lower viscosity; yet when these solutions are diluted, viscosities at low polymer concentrations are substantially higher than those of the corresponding ionomer. This desirable characteristic leads to very effective thickening behavior. A further consequence of this invention is that the resulting solutions will exhibit extremely good shear stabilities as compared to extremely high weight convention polymer solutions.
The present invention relates to the formation of water insoluble complexes of a metal sulfonated EPDM which is interacted with an EPDM containing a basic amine group. Typically, the basic amine displaying appropriate interaction will be a tertiary, secondary or primary amino group which has been grafted or otherwise reacted with various functional groups attached to the EPDM polymer molecule. One example of such an animated EPDM is that of a vinyl pyridine grafted to either an ethylene-propylene copolymer or an EPDM. Alternately under some conditions such polymers conceivably could be prepared via copolymerization routes; however, this route has generally been ineffective with conventional catalysts.
Solution of the polymer complex of a metal sulfonated EPDM with the aminated EPDM's provide very effective viscosification in a hydrocarbon diluent. For example, a polymer complex of a zinc sulfonated EPDM with vinyl pyridine grafted EP exhibits a marked decrease in dependence of viscosity on polymer concentration as compared to a sulfonated EPDM terpolymer. This behavior demonstrates a unique degree of thickening efficiency. The mechanism for this viscosification is believed to arise from an intermolecular association resulting from a coordination of the amine group with the zinc sulfonate group. This promotes an extremely effective temporary network which is very effective at viscosification. At high concentration the solution viscosity of the complex is actually less than that of the sulfonated EPDM, while at low concentration the viscosity curves are reserved. This is, in part, a consequence of ionic plasticization at high concentrations.
The resulting polymer complexes of the instant invention display a degree of isoviscous behavior with temperature as compared with either component by itself. The isoviscous behavior of these systems can be further enhanced by the addition of polar cosolvents to give viscosities which can actually increase as temperature is increased.
The instant invention is to be contrasted with the inventions described in U.S. application Ser. Nos. 547,911 and 547,908 and related copending cases which describe polymer complexes based on different polymer backbones (i.e., sulfo EPDM and styrene-vinyl pyridine). Unlike those systems, this invention is based on complexing polymers with a common backbone.
The products of those prior patent applications were based on polymers which posessed dissimilar backbones. The formation of those complexes permitted the dissolution of certain polymers normally not miscible in a solvent (or oil) through the formation of a complex. However, it was observed under some conditions when such polymer complexes were sufficiently dilute that insufficient complexing would occur and therefore one of the polymer components could (and did) phase separate. The instant invention circumvents that problem in that the polymer backbone is common to both complexing polymers. Therefore, these complexes remain soluble over all polymer concentrations and form solutions in appropriate solvents which are thermodynamically more favored. Thus, we can derive the improved thickening efficiency, shear stability, and improved VI behavior with temperature that occurs as a consequence of the complexing groups.